I’m am building a 284 win on a defiance rebel long action with BDL bottom metal (hunting rifle). Planning to shoot 180 Berger hybrid bullets using Peterson brass. GA Precision said they could chamber it using their reamer, but if I wanted to be sure it was done a certain way - to send them 3 loaded rounds of ammo or dummy rounds. I’m having a hard time determining how to come up with the right OAL based on bearing surface, boat tail length, possible donut formation, etc. I’ve gotten different ideas from searching other forums.
Barrel will be a 24” bartlein 3b contour - 8.7 twist.
To complicate things I may end up shooting 160 gr Nosler accubonds or 175 gr Nosler partitions - but neither of these is a priority.
What OAL would you recommend and why?
Thank you for your help.
As most understand, for a given caliber, the only way to make a bullet heavier is to increase its overall length. -The lead has to go somewhere. This directly influences the FB length built into the chamber. If it's a magical cartridge that is known to be extremely forgiving then the FB length will tolerate a variety of bullet weights seated at "whatever" depths.
The general strategy I try to adhere to is to keep stuff magazine tolerant, while maximizing case volume, and also try to avoid having the bearing surface of the projectile below the neck/shoulder junction of the case. Those are the constraints that have influence on "out the door" performance.
In your case you have a mile of room. The 284 is a SA cartridge. Because you have a long action receiver, you can hang the bullets out of the case to the point that they are ready to fall out of it and you will won't run out of magazine box. At this point its basically like setting up a single shot gun for F Class or whatever.
Here the general strategy again comes to mind. Set them up with the BT/Bearing feature just "north" of the case neck where it intersects with the shoulder. It's just to keep it above any doughnut that might form/be present. It's also a good idea to have at least 1 caliber of seating depth inside the neck of the case. It just helps to ensure the bullet is concentrically seated. Equally (more?) important is that it'll have sufficient surface area to hang onto the bullet securely when bouncing back and forth in an ammo box/magazine/during recoil, etc... so that your seating depths don't go do hell.
You could stretch it out a bit and gain some powder room, but keeping it a bit on the conservative side also allows for chasing the lands as you start putting miles on the barrel and this will build room in the case if the velocity starts to bleed out.
As for wanting to run a variety of bullets through the gun:
There's a trend these days it seems. I gotta have a switch barrel, switch bullet, switch twist, switch scope. . . -get my drift??? Folks who've been around awhile saw this behavior with the AR15 madness 10 years ago. I'm gonna build 10 different uppers to slap on my lower. I gotta "force multiply"...
Later this same community decided that pushing two pins out was too much work so they added more lowers to the lineup until they had complete turn key guns.
My point here is that while you may aspire to run an inventory of "X" types of bullet weights/types for a given caliber, the smarter game is to settle on something that works and then stick to it. The first question I brow beat my clients with is "what is the application?" I don't care about all the technical stuff. I want to know what you plan to use the gun for. That sets the stage so that educated decisions can be made on what parts to use and how it should be put together.
If we were talking I would ask the same question. Once I had that answer I'd encourage you to have the rifle built for that purpose. If it later decides to run the alternative bullets successfully, great. The priority though is to make sure it works for what its intended to do.
Hope this helps.
C.
